1. Field of the Invention
The present invention relates to a filter attachment machine for a filter cigarette manufacturing system, and more particularly, to a predrying apparatus incorporated in the filter attachment machine for predrying paste applied to tip paper.
2. Description of the Related Art
In recent years tobacco with mild taste has been in demand. To meet the demand, filter cigarettes each having a filter at one end of a cigarette are on the market. Filters are attached to respective cigarettes in a filter attachment machine of a cigarette manufacturing system, by wrapping a piece of tip paper around a cigarette and a filter. To this end, typically a wrapping section provided in the filter attachment machine is supplied with filter plugs each interposed between two cigarettes, as well as pieces of tip paper applied with paste.
In connection with the supply of pieces of tip paper applied with paste, the filter attachment machine has a transport path for guiding the tip paper unrolled from a paper roll to the wrapping section, and a paste applicator is arranged so as to face the transport path for applying paste to one side of the tip paper. On the downstream side of the paste applicator, a cutter is arranged for cutting the tip paper, which has been applied with paste, into pieces with a predetermined length. Also, a heater is arranged on the upstream side of the paste applicator for heating the one side of the tip paper to be applied with paste prior to the paste applying step, and a predrying apparatus is arranged on the downstream side of the paste applicator for heating the opposite side, or the non-paste side, of the tip paper to dry the paste applied to the tip paper by means of heat conducted to the paste from the tip paper.
Pieces of tip paper are supplied from the cutter to the wrapping section, where each piece of tip paper is wrapped around two cigarettes with a filter plug therebetween. Normally, by this time, the paste applied to the tip paper has been properly predried by the heater and the predrying apparatus, and thus the wrapping of tip paper pieces around cigarettes and filter plugs can usually be performed stably. Double-length filter cigarettes obtained in this manner, each connected by a piece of tip paper, are cut in the center of the filter plug, thereby obtaining individual filter cigarettes which will be finally dried, e.g., by air seasoning. The term "predry" is used herein in contrast with this "final drying."
In order to predry the tip paper as mentioned above, a heater fixedly disposed to face the tip paper transport path is conventionally used. A typical fixed heater includes a heating sheet which is affixed to a surface of a guide plate, defining part of the tip paper transport path, to produce a certain quantity of heat. Accordingly, if thermal parameters (e.g., the traveling speed of the tip paper) that affect the quantity of heat transferred to the tip paper from the fixed heater are constant, a heat quantity most suited for predrying the paste can be given to the paste-applied tip paper traveling along the transport path.
However, the thermal parameters including the tip paper traveling speed (more generally, parameters determining the predried state of paste) do not always remain fixed, but vary with changes in the operating state or operating environment of the cigarette manufacturing system.
Thus, where a constant heat quantity is transferred from the fixed heater to the tip paper, the heat quantity given to the tip paper per unit area varies if the tip paper traveling speed or the like changes, making it difficult to optimize the predried state of paste and possibly causing defective wrapping of the tip paper around cigarettes and filter plugs. Specifically, if the traveling speed of the tip paper decreases below a set speed, the paste is excessively dried, which results in reduced adhesive strength of the paste or warp of tip paper pieces, for example. Conversely, if the traveling speed of the tip paper is too fast, then the paste is insufficiently dried; in this case, paste overflows a piece of tip paper when the tip paper is wound, for example, damaging the external appearance of filter cigarettes.